1. Field of Invention
The invention relates to a collagen-based bio-absorbable wound dressing. Collagen as the albuminoid protein of the connective tissue is a component of the bodies of mammals. Collagen is ordinarily obtained from the tendons and/or skins of cattle, swine or horses. Depending on its origin and its structure, collagen is divided into different types. All types of collagen share a triple helix structure which is formed from three polypeptide chains.
2. Description of Related Art
As an endogenous material collagen is outstandingly well tolerated by the body and can be easily absorbed, and in this respect, is far superior to exogenous, synthetic materials such as cellulose. Accordingly, collagen has long been used as a wound dressing for local hemostasis, as a material for coating of tissue and bone defects, as a skin replacement in lesions and as a skin covering for large area burns. Collagen is also used as a absorbable suture material.
In addition to its good tolerance by the body and absorbability, collagen has the advantage compared to other materials that it acts hemostatically. Therefore, one application of collagen lies in dressing of wounds, especially those wounds in which some of the dermal structures or also the structures which lie under the skin have been involved. Collagen is used to treat both acute and chronic wounds. Chronic wounds are conventionally those which do not exhibit a tendency to healing even after a period of 4 to 6 weeks. Examples of chronic wounds are:                ulcus cruris (for example, due to venous or arterial conditions)        diabetic foot syndrome        decubitus, i.e., an area of the skin in which, due to excess pressure, a wound has formed, with necrosis and ulceration, often with the involvement of dermal and subdermal tissue.        
It is known that collagen can promote healing of acute and chronic wounds. In a first step, thrombocyte aggregation occurs on the collagen fibrils. The blood flow in the wound is stanched and the wound closed by collagen gel. Moreover, the collagen interacts with structures of the vascular wall and the connective tissue proteins and activates body cells which are involved in wound healing, especially the fibroblasts. In this way, the strength of the coagulation is increased. In the last stage of wound healing, the collagen is absorbed by the body by immigrated macrophages and collagenase, the wound is filled with endogenous material, and the wound surface is finally closed and smoothed.
However, wound healing can be dramatically adversely affected or prevented by wound infection, among others. Therefore, to reduce infections, wound dressings have been proposed which contain a microbicidal substance. U.S. Pat. No. 6,468,521, for example, describes a wound dressing with hydrophilic polymer carrier which is impregnated with a silver-amine complex. The silver compound has bacteriostatic and fungistatic properties. Among others, collagen is named as the carrier material. However, apparently, these silver-containing bandages are problematic in use (compare, S. Coerper, G. Gottwald, S. Beckert and H. D. Becker, “Wound healing and treatment 2004—Current status” in ZfW No. 1/04, pp. 20 to 23; page 21, right column).
While good absorbability of collagen can in general be regarded as an advantage, overly rapid absorption of collagen in wound treatment can also entail disadvantages. The speed of absorption of collagen in the body, on the one hand, depends on its structure and especially the degree of cross-linking but, on the other hand, is decisively influenced by the application site. In tissue which is well supplied with blood, for example, collagen can be completely dissolved within 2 to 3 days, while under other conditions, absorption can take 2 to 6 weeks. German Patent DE 19503336 and corresponding U.S. Pat. No. 6,117,437, for example, describe that a drug preparation with a depository effect in which the drug is administered on a collagen vehicle which is mixed with chlorohexidine hydrochloride completely decomposes in the body after 30 minutes. In wound dressings, however, it is often desirable that they remain on the wound for at least 72 hours. Overly frequent changing of the bandage entails not only the danger that the wound will be torn open again, but also increases the danger of infection. Therefore, there is a demand for a wound dressing of collagen which is not completely absorbed even in tissue, with good blood supply, over an interval of at least 3 days.
German Patent Application DE 10132817 A1 discloses a wound treatment agent in the form of a solution or a gel that contains, in aqueous solution, polyhexamethylene biguanide and at least one surfactant. The surfactant is a glycine derivative and/or a sulfosuccinate and/or an amide based on an unbranched fatty acid. The surfactant is preferably a betaine and, in particular, an amidoalkyl betaine of a fatty acid.